The present invention relates to golf balls and, in particular, to golf balls having at least one layer formed of a polymer blend formed of a polymer blend comprising at least one oxa ester or a blend of at least one saponified polymeric material and at least one oxa ester. The saponified polymeric material may be unmodified, or may contain at least one pendant functional group that is grafted to the polymer chain. The layer, which may be foamed or unfoamed, may be located in any of the cover or core of the ball or in a mantle layer located between the cover and the core.
Three-piece, wound golf balls with balata covers are preferred by many expert golfers. These balls provide a combination of distance, high spin rate, and control that is not available with other types of golf balls. However, balata is easily damaged in normal play, and, thus, lacks the durability required by the average golfer.
In contrast, amateur golfers typically prefer a solid, two-piece ball with an ionomer cover, which provides a combination of distance and durability. Because of the hard ionomer cover, these balls are almost impossible to cut, but also have a very hard xe2x80x9cfeelxe2x80x9d, which many golfers find unacceptable, and a lower spin rate, making these balls more difficult to draw or fade. The differences in the spin rate can be attributed to the differences in the composition and construction of both the cover and the core.
Many attempts have been made to produce a golf ball with the control and feel of a wound balata ball and the durability of a solid, two-piece ball, but none have succeeded totally. In various attempts to produce an ideal golf ball, the golfing industry has blended hard ionomer resins (i.e., those ionomer resins having a hardness of about 60 to 66 on the Shore D scale, as measured in accordance with ASTM method D-2240) with a number of softer polymeric materials, such as softer polyurethanes. However, the blends of the hard ionomer resins with the softer polymeric materials have generally been unsatisfactory in that these balls exhibit numerous processing problems. In addition, the balls produced by such a combination are usually short on distance.
While different blend combinations of species of one variety of polymer, such as prior art ionomers, i.e., copolymers of an olefin and an xcex1,xcex2-unsaturated carboxylic acid, have been successfully used in the prior art, different polymers, such as carboxylic acid based ionomers and balata or other non-ionic polymers have not been successfully blended for use in golf ball covers. In general, prior art blends of polymer components are immiscible, i.e., heterogeneous on a microscopic scale, and incompatible, i.e., heterogeneous on a macroscopic scale, unless strong interactions are present between the polymer components in the mixture, such as those observed between carboxylic acid based ionomers and other polymers containing carboxylic acid groups. In particular, this lack of compatibility exists when an ionomer is blended with a polyolefin homopolymer, copolymer, or terpolymer that does not contain ionic, acidic, basic, or other polar pendant groups, and is not produced with a metallocene catalyst. These mixtures often have poor tensile strength, impact strength, and the like. Hence, the golf balls produced from these incompatible mixtures will have inferior golf ball properties such as poor durability, cut resistance, and so on. In contrast, a compatible blend may be heterogeneous on a microscopic scale, but is homogeneous on a macroscopic scale, and, thus, has useful golf ball properties.
In this regard, U.S. Pat. No. 5,397,840 discloses golf ball covers including a blend of xe2x80x9cionic copolymersxe2x80x9d and xe2x80x9cnon-ionic copolymersxe2x80x9d. However, the xe2x80x9cionic copolymersxe2x80x9d are defined as copolymers of an xcex1-olefin and a metal salt of an xcex1,xcex2-unsaturated carboxylic acid, and the xe2x80x9cnon-ionic copolymersxe2x80x9d are copolymers or terpolymers containing ethylene or propylene and acrylic or methacrylic acid monomers. Therefore, strong interactions exist between the metal salts of the xe2x80x9cionic copolymersxe2x80x9d and the acrylic or methacrylic acid monomers of the xe2x80x9cnon-ionic copolymersxe2x80x9d that allow compatible blends to be formed. These interactions do not exist in prior art blends of ionomers and polymers that are truly non-ionic or non-polar.
U.S. Pat. No. 5,616,640 to Harris et al. discloses golf ball cover compositions comprising an oxa acid compound having the formula 
which may be blended with prior art, carboxylic acid based ionomers to provide golf balls having an excellent spin rate and good shear resistance.
U.S. Pat. No. 5,607,687 to Bezwada et al. discloses polymer blends containing absorbable polyoxaesters and blends of polyoxaesters and other biologically compatible polymers for use in surgical devices.
U.S. Pat. No. 5,869,578 to Rajagopalan discloses golf balls comprising xe2x80x9csaponified ionomersxe2x80x9d, i.e., ester based ionomeric polymers produced by carrying out a hydrolysis or saponification on copolymers containing pendant ester groups to form an ionomeric polymer that is less hydrophilic than typical carboxylic acid based ionomers to provide golf balls having enhanced physical properties when compared to prior art golf balls.
Co-pending Application Ser. No. 09/132,193 U.S. Pat. No. 6,255,361 discloses golf balls comprising compatible blends of oxa acids and saponified ionomers.
However, there is no known disclosure of golf balls comprising oxa esters or blends of oxa esters and other polymers, such as saponified ionomers.
Hydrolysis or saponification of alkyl acrylate units in a crosslinkable polymer chain is disclosed by Gross in U.S. Pat. No. 3,926,891. In U.S. Pat. No. 3,970,626, Hurst discloses heating a mixture of an alkali metal hydroxide, a thermoplastic ethylene-alkyl acrylate copolymer and water to saponify the acrylate units and form an aqueous emulsion.
A different approach to hydrolysis or saponification of an ethylene-alkyl acrylate copolymer is disclosed by Kurkov in U.S. Pat. No. 5,218,057, in which the copolymer is mixed with an aqueous solution of an inorganic alkali metal base at a temperature sufficient for saponification to take place and at which the copolymer undergoes a phase change.
All of the prior saponification methods discussed above require that the polymer component be in contact with water, either by conducting the reaction in an aqueous medium or by adding an aqueous solution to the polymer. However, nonaqueous inorganic alkali metal base solutions, e.g., containing an alcohol or polyethylene glycol solvent, are disclosed by U.S. Pat. No. 5,554,698 to Wang et al., although aqueous solutions are disclosed to be preferred.
McClain, in U.S. Pat. No. 4,638,034, discloses a process whereby ethylene-acrylic acid copolymers or their ionomers are prepared from ethylene-alkyl acrylate copolymers by saponifying the latter in the melt with metal hydroxides to form an ionomer and a by-product, i.e., alkanol, then optionally acidifying the ionomer to form the free acid copolymer.
The processes disclosed by the Kurkov, McClain and Wang references, in particular, are incapable of providing optimal product quality since blending and saponifying in a single operation as taught by the subject references leads to rapid saponification, with a concurrent rapid increase in melt viscosity. Due to this rapid increase in melt viscosity, the resultant mixture is non-uniform and therefore the material properties of products made from this material are not consistent throughout the product. U.S. Pat. No. 5,869,578 to Rajagopalan, a patent that issued from one of the parent applications of the present invention, overcame the above deficiencies.
A need exists in the golf ball art for highly durable golf balls, which have improved performance, and may be tailored to have virtually any combination of feel and spin rate. The present invention provides such a golf ball.
The present invention is directed to a golf ball having least one layer, the layer formed of a polymer blend comprising at least one oxa ester. Useful oxa esters include
(a) monoesters of the formula: 
(b) diesters of formula: 
wherein n is an integer greater than or equal to 1, preferably from 1 to 27, R1 and R3 are typically CH3, but may be any organic moiety selected from the group consisting of a linear or branch chained alkyl, a substituted or unsubstituted carbocyclic or heterocyclic groups, and R2 is H or an organic moiety selected from the group consisting of linear and branch chained alkyl, substituted and unsubstituted carbocyclic, and heterocyclic groups;
(c) polymers of the formula 
(d) polymers of formula 
and (e) polymers of formula 
where R4 and R5 are independently selected from the group consisting of hydrogen or an alkyl group containing from 1 to 8 carbon atoms;
a is an integer in the range of from 1 to about 2,000 and preferably from 1 to about 1000;
b, d and g are independently an integer in the range of from about 1 to about 10,000 and preferably is in the range of from about 10 to about 1,000 and most preferably in the range of from about 50 to about 200;
c is an integer in the range from 1 to 2000;
e is an integer in the range of from 1 to about 6,000, preferably from 1 to about 1,200, most preferably from about 1 to about 250;
f is an integer from about 1 to about 200;
R6 is an alkylene containing from 2 to 12 carbon atoms or is an oxyalkylene group of formula:
xe2x80x94[(CH2)hxe2x80x94Oxe2x80x94]ixe2x80x94(CH2)jxe2x80x94
where h is an integer in the range of from about 2 to about 5, i is an integer in the range of from about 0 to about 2,000 and preferably from 0 to 12, and j is an integer in the range of from about 2 to about 5;
R7 is an alkylene unit containing from 2 to 8 methylene units;
R8 is selected from the group consisting of xe2x80x94C(R9)(R10)xe2x80x94, xe2x80x94(CH2)3xe2x80x94Oxe2x80x94, xe2x80x94CH2xe2x80x94CH2xe2x80x94Oxe2x80x94CH2xe2x80x94, xe2x80x94CR11Hxe2x80x94CH2xe2x80x94, xe2x80x94(CH2)4xe2x80x94, xe2x80x94(CH2)kxe2x80x94Oxe2x80x94C(O)xe2x80x94, and xe2x80x94(CH2)kxe2x80x94C(O)xe2x80x94CH2xe2x80x94;
R9 and R10 are independently hydrogen or an alkyl containing from 1 to about 8 carbon atoms;
R11 is hydrogen or methyl;
k is an integer of from about 2 to about 6;
G represents the residue minus from 1 to L hydrogen atoms from the hydroxyl groups of an alcohol previously containing from 1 to about 200 hydroxyl groups; and
L is an integer from about 1 to about 200.
Typically a layer of a golf ball comprising the present invention has a hardness of at least 15 Shore A, a flexural modulus of at least 500 psi, and a specific gravity of at least 0.7. Preferably, the flexural modulus of at least 500 to about 300,000 psi.
A golf ball comprising the present invention has an Atti compression of at least 50 and a coefficient of restitution of at least 0.7. Preferably, the Atti compression of the golf ball is at least 60 to about 100.
Golf balls in accordance with the invention preferably have a cover thickness of at least 0.03 inch to about 0.125 inch and at least 60 percent dimple coverage, and a core 20 diameter of at least 0.5 to about 1.63 inches. Where the golf ball of the present invention further comprises at least one optional mantle or intermediate layer, the mantle or intermediate layer has a thickness of at least 0.02 inches.
Golf balls of the present invention preferably have a cover layer hardness of about 40 Shore D to about 70 Shore D and a flexural modulus of about 10,000 to about 100,000 psi, an intermediate layer hardness of about 20 Shore D to about 70 Shore D and a flexural modulus of about 500 to about 100,000 psi and a core layer hardness of about 40 Shore A to about 70 Shore D and a flexural modulus of about 500 to 150,000 psi.
Any of the cover, the core or the center, or the at least one optional mantle or intermediate layer may comprise a density adjusting filler material to increase or decrease the density. The density adjusting filler material may be a metallic powder or a metallic oxide derivative. Preferably, the metallic powder is either titanium, tungsten, tin or copper powder and the metallic oxide derivative is an oxide derivative of titanium, tungsten, copper or tin.
In addition, any of the cover, the core or the center, or the at least one optional mantle or intermediate layer further comprises a wound tensioned elastomeric material wherein the tensioned elastomeric material further comprises natural or synthetic elastomers or blends thereof An example of a synthetic elastomer is LYCRA. The center may be solid, fluid filled or hollow.
Typically, the oxa ester is present in a polymer blend in an amount of from about 1 to about 35 parts, preferably from about 1 to about 25 parts, and most preferably from about 1 to about 15 parts, based on 100 parts of the polymer blend.
Preferably, the polymer blend further comprises at least one saponified polymer. Typically, the saponified polymer/oxa ester blend comprises from about 1 to about 35 parts of the oxa ester and from about 99 to about 65 parts of the saponified polymer, based on 100 parts of the polymer blend. Preferably, the saponified polymer/oxa ester blend comprises from about 1 to about 25 parts of the oxa ester and from about 99 to about 75 parts of the saponified polymer, and, most preferably from about 1 to about 15 parts of the oxa ester and from about 99 to about 85 parts of the saponified polymer, based on 100 parts of the polymer blend.
The saponified polymer component of this invention has a Shore D hardness of at least 15, as measured by ASTM method D-2240, a flexural modulus, as measured by ASTM method D-790, of at least 500 psi, preferably about 1000 psi to about 100,000 psi, a specific gravity of at least 0.7, preferably from about 0.75 to about 1, a dynamic shear storage modulus (Gxe2x80x2) at 23xc2x0 C., as described in ASTM D 4092-90, ASTM D 5279-93, and ASTM D 4065-94, of at least 104 dynes/cm2, preferably about 106 to about 1010 dynes/cm2, and most preferably from about 106 to about 109 dynes/cm2, and a loss tangent (tan xcex4) of no more than about 1, preferably, no more than about 0.1, and most preferably from about 0.001 to about 0.01 at 23xc2x0 C.
Typically, the saponified polymer comprises a first olefinic, monomeric component having from 2 to 8 carbon atoms, a second monomeric component comprising an unsaturated carboxylic acid based acrylate class ester having from 4 to 22 carbon atoms and at least one ester group, wherein at least a portion of the ester groups have been saponified with an inorganic metal base, and, optionally, a third monomeric component selected from the group consisting of carbon monoxide, sulfur dioxide, an anhydride monomer, an unsaturated monocarboxylic acid, an olefin having from 2 to 8 carbon atoms and a vinyl ester or a vinyl ether of an alkyl acid having from 4 to 21 carbon atoms. Metal bases useful in the invention include, but are not limited to, those comprising at least one metallic cation, selected from the group consisting of lithium, sodium, potassium, cesium, magnesium, calcium, barium, manganese, copper, zinc, titanium, tungsten, zirconium, and aluminum, and at least one anion, selected from the group consisting of hydroxide, alkoxide, acetate, carbonate, bicarbonate, oxide, formate, and nitrate.
The first monomeric component of the saponified polymer is typically an xcex1-olefin monomer having a terminal point of unsaturation, such as ethylene, and preferably has the formula: 
where R12 is hydrogen or an alkyl group; and R13 is hydrogen, lower alkyl, carbocyclic, or aromatic. Typically, the first monomeric component comprises from about 1 to about 99 percent by weight, preferably from about 10 to about 95 percent by weight, and, most preferably, from about 10 to about 70 percent by weight of the total polymer weight.
Typically, the second monomeric component of the saponified polymer is an unsaturated acrylate class ester having the formula: 
where R14 is hydrogen or an alkyl group; R15 is hydrogen, lower alkyl, carbocyclic, or aromatic; and R16 is selected from the group consisting of CnH2n+1, for n=1 to 18 and phenyl. From 0 to 5 H within R16 can be replaced by substituents selected from the group consisting of COOH, SO3H, NH2, succinic anhydride and their salts, or R16 can be replaced by substituents selected from the group consisting of F, Cl, Br, I, OH, SH, epoxy, silicone, lower alkyl esters, lower alkyl ethers, and aromatic rings, wherein optionally R15 and R16 can be combined to form a bicyclic ring. Typically, the second monomeric component comprises from about 99 to about 1 percent by weight, preferably from about 90 to about 5 percent by weight, and, most preferably, from about 90 to about 30 percent by weight of the total polymer weight.
Useful third monomeric components of the saponified polymer include, but are not limited to, monomers having the formulae: 
where R17, R18, R19and R22 are independently hydrogen, lower alkyl, carbocyclic or aromatic;
R20 and R23 are independently hydrogen or lower alkyl;
R21 is hydrogen, or is selected from the group consisting of CnH2n+1, for n=1 to 18 and phenyl, in which from 0 to 5 H within R21 can be replaced by substituents selected from the group consisting of COOH, SO3H, NH2 and their salts, or R21 can be replaced by substituents selected from the group consisting of F, Cl, Br, I, OH, SH, silicon, lower alkyl esters, lower alkyl ethers and aromatic rings, wherein optionally R20 and R21 can be combined to form a bicyclic ring;
R24 is hydrogen, or is selected from the group consisting of CnH2n+1, for n=1 to 18 and phenyl, in which from 0 to 5 H within R24 can be replaced by substituents selected from the group consisting of COOH, SO3H, NH2 and their salts, or R24 can be replaced by substituents selected from the group consisting of F, Cl, Br, I, OH, SH, silicon, lower alkyl esters, lower alkyl ethers and aromatic rings, wherein optionally R23 and R24 can be combined to form a bicyclic ring. Typically, the optional third monomeric component accounts for up to about 49 percent by weight of the total polymer weight
The saponified polymer, which may be isotactic, syndiotactic, and atactic polymers and combinations thereof, may further comprise at least one functional pendant group added to the polymer by sulfonation, carboxylation, addition of an amine or hydroxy, or by grafting an ethylenically unsaturated monomer onto the saponified polymer using a post-polymerization reaction, and is present in an amount of between about 1 to about 50 percent by weight, preferably, between about 1 and about 25 percent by weight, and, most preferably, between about 1 and about 15 percent by weight, based on the total weight of the polymer. Preferably, the functional pendant group is an anhydride having the formula: 
wherein:
R25 and R26 are the same or different and are selected from the group consisting of hydrogen, linear or branched chain alkyl and substituted or unsubstituted carboxylic groups.
Typically, the golf ball of the invention comprises a cover, a core, and, optionally, an intermediate layer situated between the cover and the core, where the layer may form a portion of any of the cover, the core, and the intermediate layer, and may have a foamed structure. Cores useful in the invention may be of any type known in the art found in golf balls, such as wound cores, solid cores, hollow cores, and cores filled with a fluid, and often comprise cis-polybutadiene.
Polymer blends useful in the invention may further comprise oxa acids, block copolymers of a poly(ether-ester), block copolymers of a poly(ether-amide), styrene-butadiene-styrene block copolymers, styrene-(ethylene-propylene)-styrene or styrene-(ethylene-butylene)-styrene block copolymers, styrene-butadiene-styrene block copolymers grafted with at least one of maleic anhydride or a sulfonic graft or functionality, olefinic copolymers, metallocene catalyzed polymers, block poly(urethane-ester), block poly(urethane-ether), block poly(urethane-caprolactone), polyethylene glycol, polycaprolactone, polycaprolactam, polyesters, polyamides, ethylene-propylene-(diene monomer) terpolymers and their sulfonated or carboxylated derivatives, and PP/EPDM and dynamically vulcanized rubbers, as well as conventional ionomers, such as those comprising an xcex1-olefin, an xcex1,xcex2-unsaturated carboxylic acid, and, optionally, an acrylate class ester as a softening monomer, wherein at least a portion the carboxylic acid groups on the polymer have been neutralized with at least one metal atom.
The invention is further directed to a method for forming a golf ball. The method of the invention comprises forming a polymer blend, which comprises at least one oxa ester; and forming at least one layer of a golf ball from the polymer blend. The method may further comprise forming a polymer comprising a first olefinic monomeric component having from 2 to 8 carbon atoms and a second monomeric component comprising an unsaturated carboxylic acid based acrylate class ester having from 4 to 22 carbon atoms; applying a sufficient amount of heat to the polymer to convert the polymer to a substantially molten state; forming a mixture by adding an inorganic metal base to the molten polymer; saponifying the mixture to form a saponified polymer, wherein a sufficient amount of the inorganic metal base is added to the molten polymer in forming the mixture to obtain a degree of saponification of the polymer ranging between about 1 and 50 percent; and blending the saponified polymer with the at least one oxa ester to form the polymer blend.
Preferably, the mixture of the inorganic metal base and the molten polymer is formed at a temperature such that the mixture has a viscosity that remains substantially unchanged from that of the molten polymer. In addition, the polymer may be formed with a third monomeric component, selected from the group consisting of carbon monoxide, sulfur dioxide, an anhydride monomer, an unsaturated monocarboxylic acid, an olefin having from 2 to 8 carbon atoms, and a vinyl ester or a vinyl ether of an alkyl acid having from 4 to 21 carbon atoms.